Optical Disk Drive Servo System Using Dual Disturbance Observer

Transcription

1 ICCA5 Jue -5, KINTEX, Gyeoggi-Do, Korea Optical Dik Drive ervo ytem Uig Dual Diturbace Oberver ag Ha Lee*, Dog eul Jeog ** ad Chug Choo Chug *** * Departmet of Electroic ad Computer Egieerig, Hayag Uiverity, eoul 33-79, Korea (Tel : ; trage77@ihayagackr) ** Departmet of Electroic ad Computer Egieerig, Hayag Uiverity, eoul 33-79, Korea (Tel : ; djeog@ihayagackr) *** Diviio of Electrical ad Biomedical Egieerig, Hayag Uiverity, eoul 33-79, Korea (Tel : ; cchug@hayagackr) Abtract: Uig diturbace oberver (DOB) i effective i ehacig the performace of dyamic ytem i the preece of diturbace Recetly the defiitio of diturbace ha bee expaded to modelig ucertaity icludig parameter variatio, iteral diturbace Variou tructure of DOB have bee propoed to improve eitivity of ytem for better diturbace rejectio performace However i the cae of improvemet of eitivity fuctio, it ted to brig poor traiet repoe due to cro-couplig ad phae lag Furthermore it could be very eitive to meauremet oie due to icreaed peak of complemetary eitivity fuctio I thi paper, a dual diturbace oberver (Dual-DOB) i propoed to reduce the effect of uch cro-couplig It i poible for u to improve the eitivity fuctio with additioal exteral DOB with hardly affectig complemetary eitivity fuctio Thu it i able to have robute agait meauremet oie ice we are able to deig DOB of iteral ad exteral loop idepedetly, we could prevet traiet repoe quality from degradig while improvig the eitivity fuctio The propoed Dual-DOB i applied to a commercial optical dik drive trackig ervo ytem The experimetal reult how that the Dual-DOB i a effective method i rejectig the diturbace a well a improvig the trackig performace Keyword: Trackig cotrol, diturbace oberver, optical dik drive, Dual-DOB INTRODUCTION Diturbace oberver (DOB) ha bee kow to compeate effectively by obervig it from the view poit of liear ytem After DOB wa propoed by Ohihi [, ], it deig method ad performace have bee aalyzed theoretically [3] Recetly the defiitio of diturbace ha bee expaded to modelig ucertaity icludig parameter variatio, iteral diturbace uch a torque diturbace ad frictio The purpoe of uig DOB i to ehace the performace of the ytem by obervig ad cacelig uch udeirable diturbace [4, 5] I DOB, the diturbace rejectio performace deped o Q-filter (low pa filter) order ad it robute agait modelig ucertaity deped o relative degree ad deomiator order of Q-filter [6] DOB i alo applied to robot ytem, high peed ytem, preciio poitio cotrol, optical dik drive ytem [7]-[] Diturbace i optical dik drive ytem uch a CD ad DVD are compoed of dik urface vibratio, dik eccetricity ad actuator reoace I trackig ervo, optical pot ha to follow track with le tha ± µ m trackig error Thu the above metioed diturbace caue it difficult to track follow uch arrow track pitch i high peed ad high deity ODD ytem [] It i propoed that DOB i very effective i rejectig the diturbace i ODD ytem [, ] However, oly the trackig error i available i ODD ytem itead of referece iput or output To overcome thi problem, there were ome attempt Oe method i to ue a additioal eor to etimate referece iput ad to apply the etimated referece iput to DOB [] Aother method i to apply a error baed DOB (EDOB) which i a modified DOB [] without uig additioal eor to meaure the referece iput Beide thee method, variou type of DOB, to improve diturbace rejectio performace ad eitivity, were propoed for example PAC, RIC, MPEC ad IMC There ha bee a trial to reduce cro-couplig effect ad improve eitivity by adjutig gai betwee PAC (Paive Adaptive Cotroller) ad DOB RIC (Robut Iteral loop Compeator) ca traform DOB to uity dc gai equivalet feedback with feed-forward It performace i determied by the badwidth of Q-filter [9] MPEC (Multi loop Perturbatio Compeator) i aother compeator deig method with multi loop tructure igle loop DOB ha a limitatio for the compeatio value of diturbace rejectio due to time-delay ad phae lag We are able to get improved performace by addig additioal exteral loop ice the icomplete diturbace rejectio i the ier loop ca be compeated at the exteral loop DOB Thi multi loop tructure improve ytem robute [3] IMC (Iteral Model Cotroller) compeate ucompeated diturbace of iteral loop at exteral loop [4] Although IMC improve eitivity fuctio by multiplyig it exteral loop, it i very eitive to meauremet oie due to icreae of complimetary eitivity fuctio peak The multi loop DOB, which are propoed up to ow, ted to brig poor traiet repoe due to cro-couplig iter loop ad phae lag [3] Therefore, there eed trade-off betwee eitivity fuctio i frequecy domai ad traiet repoe i time domai I thi paper, Dual-DOB i propoed to maitai diturbace rejectio performace of former multi loop DOB, reducig cro-couplig effect, ad robut agait meauremet oie The Dual-DOB tructure coit of iteral loop ad exteral loop Actually, it i imilar to IMC tructure however it ha a differet deig method of exteral loop Although IMC could improve diturbace rejectio performace by addig it exteral loop, it i very eitive to meauremet oie due to the icreaed peak of complimetary eitivity fuctio Therefore, i thi paper to reolve thi problem we ue a differet omial model for deigig the exteral loop DOB Thi i a major differece from IMC tructure A a reult, the Dual-DOB propoed i thi paper improve the eitivity fuctio at low frequecy without icreaig the peak of the eitivity fuctio By deigig DOB of iteral ad exteral loop idepedetly, we could avoid degradig performace of traiet repoe while improvig the eitivity fuctio The propoed

2 ICCA5 Dual-DOB i applied to a trackig ytem of commercial optical dik drive The experimetal reult how that the Dual-DOB i a effective method i rejectig the diturbace a well a improvig the trackig performace PRINCIPLE AND ANALYI OF DITURBANCE OBERVER Priciple of Diturbace Oberver The DOB ytem reject diturbace by ijectig ito the cotrol iput a compeatio value, which i the differece betwee the commaded cotrol iput to the plat ad the plat output filtered by the ivere of the omial plat P (), ie P (), a how i Fig If uity dc gai Q-filter i ued, the compeatio value of DOB become d i low frequecy badwidth a i Eq () Without coideratio of ucertaity of plat modelig, the compeatio value ca completely reject torque diturbace i the iput ad output diturbace Q( ) [ ] lim d = u d P( ) P ( ) u P d d P d i out i out () However, due to P () geerally cotai pure differetial term, ofte it i ot phyically realizable Thu, it i commo to ue Q-filter with P () I additio uig Q-filter reduce it le eitive to meauremet oie Thi Q-filter ha typically the characteritic of low pa filter (LPF) with a uity dc gai I thi paper, biomial Q-filter i ued a a low pa filter [5] Q m i ami ( τ ) i= m!, a m mi ( τ ) ( m ) = = i!! i () whereτ i filter time-cotat, a mi are biomial coefficiet, m i the deomiator order ad i the umerator order of filter atifyig m> The higher order of the filter i, the better performace of low pa filter ca be obtaied However, high-order filter could have a advere effect o cotroller performace due to phae lag O the other had, the badwidth of Q-filter ha alo a effect o ytem repoe A the badwidth of Q-filter i icreaed, we ca reject fat udeirable diturbace Thu Q-filter i a importat factor i the performace of DOB [6] Aalyi of Applied Diturbace Oberver ytem It i ot eay to aalyze the performace of DOB through uual expaio of trafer fuctio i the preece of modelig ucertaity eve though we could aalyze the performace of DOB from characteritic equatio of trafer fuctio However, if we elimiate the real plat from the trafer fuctio by uig a ew parameter δ () repreetig ytem ucertaity, it could be eay to maipulatio equatio ad a ituitioal aalyi i further poible [3] δ ( ) i deoted a i Eq (3) ad there i a cloe affiity betwee δ ( ) ad M () which i multiplicative modelig ucertaity r Jue -5, KINTEX, Gyeoggi-Do, Korea C () - - d u di Q () P () - dout QP () () Fig ytem tructure of DOB The real plat i defied a P () = P() [ M() ] P () P () where M () = P () The δ ( ) i defied uch that P () δ () = M() P () P() P() P() = P () P() P () P() = P () y (3) The total iput-to-output relatiohip from the referece igal ( r ), the torque diturbace ( d ), the output diturbace ( d ), ad the meauremet oie ( ) to the out output are expreed i Eq (4) y= G () r () d () d T () (4) Dob Dob _ i i Dob _ out out Dob _ oie where CPP () () () G () = Dob [ Q ( )] P( ) QP ( ) ( ) CPP ( ) ( ) ( ) [ Q ( )] PP ( ) ( ) () = Dob _ i [ Q ( )] P( ) QP ( ) ( ) CPP ( ) ( ) ( ) [ Q ( )] P( ) () = Dob _ out [ Q ( )] P( ) QP ( ) ( ) CPP ( ) ( ) ( ) [ Q () CP () () ] P () T () = Dob _ oie Q( ) P( ) Q( ) P( ) C( ) P( ) P( ) [ ] i (5) (6) (7) (8) For implicity ad ituitioal aalyi of Eq (5)~(8), we rewrite thee a Eq (9)~() uig parameter, δ ( ) G T Dob Dob _ i CP () () () = δ () Q () CP () () Dob _ out Dob _ oie [ ] [ Q ( )] P( ) [ ] [ Q ( )][ δ ( ) ] [ ] [ Q] [ ] () = δ () Q () CP () () () = δ () Q () CP () () ( ) CP ( ) ( ) () = δ () Q () CP () () (9) () () () If we aume that diturbace exit oly i low frequecy rage i Eq (9)~(), cloed loop ytem act like omial

3 ICCA5 model ytem i low frequecy due to Q-filter implemet a low pa filter with a uity dc gai Jue -5, KINTEX, Gyeoggi-Do, Korea omial model, G Dob ( ) r - di C () P() - - Q () - d out QP () () η y P () db ω Q () - QG () DOB () Fig ytem tructure of Dual DOB 3 ANALYI OF DUAL-DOB TRUCTURE 3 tructure of Dual-DOB Variou tructure of DOB have bee propoed to improve eitivity of ytem for better diturbace rejectio performace [3, 9,, 4, 5] Due to cro-couplig of multiple DOB tructure, the performace of DOB eed trade-off betwee eitivity of frequecy domai ad traiet repoe of time domai I thi paper, the Dual-DOB i propoed to reduce the effect of cro-couplig By deigig DOB of iteral ad exteral loop idepedetly, we could prevet the decreaig of traiet repoe quality durig improvemet the eitivity fuctio The Dual-DOB tructure add the exteral loop to the ytem icludig iteral DOB loop a how i Fig It i imilar to IMC (Iteral Model Cotroller) tructure which i multiple DOB but Dual-DOB ha differet deig method of exteral loop Although IMC improve eitivity fuctio by multiplyig it exteral loop, it i very eitive to meauremet oie due to icreaig of complimetary eitivity fuctio peak [4] Therefore we deiged omial ytem model ued fro deigig of exteral loop, differetly from IMC tructure i order to improve thi problem A covetioal DOB ytem ha a limitatio of diturbace rejectio performace due to time delay ad modelig ucertaity Iteral loop of Dual-DOB ue a covetioal DOB which ue a omial model a how i Fig 3(a) To compeate diturbace ucompeated i the iteral loop due to ytem modelig ucertaity ad icomplete compeatio, the exteral loop DOB ue the deired cloed loop trafer fuctio a a omial plat a Fig 3(b) Thi i the key feature of the Dual-DOB propoed i thi paper Becaue the exteral DOB i deiged baed o omial cloed loop, it oberve the behavior of the iteral cloed loop ytem icludig the iteral DOB ad compeate ucompeated diturbace Thu we ca get ehacemet of eitivity applyig Dual-DOB tructure By deigig Dual-DOB of iteral ad exteral loop idepedetly, we could avoid degradig traiet repoe performace while improvig the eitivity fuctio i low frequecy rage 3 Aalyi of Dual-DOB ytem Dual-DOB coit of iteral DOB ad exteral DOB While iteral DOB loop ue typical omial model of plat a covetioal DOB ytem, exteral loop DOB i deiged by applyig the deired cloed loop trafer fuctio Eq (9) icludig iteral DOB a a omial plat Due to the modelig ucertaity, we caot ue Eq (9) a the trafer fuctio If we approximate Eq (9) a Eq (3) i low frequecy rage, however we could aume cloed loop G () DOB (a) Nomial model of iteral loop DOB db (b) Nomial model of exteral loop DOB Fig 3 Bode of Dual-DOB omial Model * CP () () GDob() = lim GDob () = (3) δ ( ) CP ( ) ( ) I the ame way i ectio, we ca rewrite the trafer fuctio, Eq (4)~(7), uig parameter δ () from the cotrol referece, the torque diturbace, the output diturbace, ad the meauremet oie to the output of the Dual-DOB ytem [3] G T Dual CP () () () = δ () Q () CP () () [ ] [ Q ( )] P ( ) [ ] [ Q ( )] [ δ ( ) ] [ ] [ Q] [ ] () = δ () Q () CP () () Dual _ i () = δ () Q () CP () () Dual _ out ( ) CP ( ) ( ) () = δ () Q () CP () () Dual _ oie ω (4) (5) (6) (7) All the trafer fuctio of the Dual-DOB how improvemet of eitivity fuctio i low frequecy rage with hardly affectig complemetary eitivity fuctio i high frequecy rage Compared to covetioal DOB trafer fuctio i ectio, we ee that ( Q) term of covetioal DOB trafer fuctio are replaced with ( Q) i deomiator i Dual-DOB The ucertaity term δ are multiplied by ( Q) ice Q-filter gai i equal to or le tha i all frequecy rage, Dual-DOB ytem i more robut agait modelig ucertaity tha covetioal DOB ytem I the view poit of torque diturbace ad output diturbace eitivitie, deomiator term of trafer fuctio ( Q) chage to ( Q) Thi chage mea that ehacemet of diturbace rejectio performace agait to diturbace i the low frequecy rage Alo, ( Q), the deomiator term of meauremet oie trafer fuctio, chage to ( Q) I geeral there i improvemet i diturbace rejectio performace of DOB ytem becaue the ucertaity term δ

4 ICCA5 i weighted by ( Q) Multiple DOB ytem are able to reduce eitivity fuctio i low frequecy rage but they brig poor traiet repoe due to cro-couplig However Dual-DOB ytem provide low eitivity fuctio without loig traiet performace compared to previou multi loop DOB ytem ice Dual-DOB i deiged to miimize the cro-couplig amog multiple loop Example will be how i the ext ubectio 4 IMULATION AND EXPERIMENT 4 Optical Dik Drive ytem For verifyig the Dual-DOB performace, we et up a experimet eviromet with a commercial DVD combo player from LG electroic The pick-up of the optical dik drive i coited of a coare actuator ad a fie actuator a how i Fig 4 A teppig motor i ued for coare actuatio ad a VCM (Voice Coil Motor) i ued for fie oe To get the omial model of plat, we meaured the gai from the iput of the VCM driver to the output of RF-AMP Thu the omial plat of track followig ytem i approximated a a ecod order ytem a i Eq (8) P () = K ξω ω (8) where ω i reoace frequecy, ξ i dampig ratio, K i the dc gai from the iput of VCM driver to the output of RF-AMP I the model parameter ω i 367rad/ec, ξ i 7 58, ad K i 43 pidle Motor Pick-up Objective Le Coare Actuator Fig 4 ytem tructure of ODD ytem Dik Ma-prigdamper Fie Actuator For experimetally verifyig the omial model, we draw bode plot of cloed loop ytem uig HP3567A Dyamic igal Aalyzer I imulatio ad experimet, we ue the omial model of Fig 5 4 Optical Dik Drive ytem A metioed before, a liear cotroller C () i deiged baed o the omial model uig the property of DOB The liear cotroller i deiged uig lead-lag compeatio a i Eq (9) The Q-filter i biomial low pa filter with ecod order of deomiator adτ i C () = (9) Jue -5, KINTEX, Gyeoggi-Do, Korea Q() = Frequecy Repoe of Trackig Actuator Magitude [db] Phae [Degree] Frequecy [Hz] DA Model 3 4 Frequecy [Hz] Fig 5 Frequecy Repoe of Trackig Actuator () Uig Biliear traformatio method, cotroller ad C (), Q () are traformed to dicrete time cotroller with µ amplig time ice oly poitio error igal i available i optical drive ytem, we deig the cotroller with zero referece iput The Fig 6 how improvemet of eitivity fuctio i the equece of lead-lag cotroller, lead-lag cotroller with DOB, ad lead-lag cotroller with DOB ad that with Dual-DOB It how little differece betwee lead-lag cotroller ad lead-lag oe with DOB i ~Hz rage The badwidth of the Q-filter i choe low ice diturbace exit at very low frequecy (Hz) while the meauremet oie i too large compared to trackig error igal The peak of eitivity fuctio of Dual-DOB doe ot icreae compared to geeral multi loop DOB It i eceary for the eitivity fuctio ot to have high peak to avoid poor traiet repoe i time domai Fig 7 how complemetary eitivity fuctio A we ee i the figure Dual-DOB ha almot the ame complemetary eitivity fuctio i pite that it i a multi loop ytem Thu the performace of Dual-DOB to meauremet oie i ot deteriorated Fig 8 how imulatio reult Fig 8(a) i the output diturbace ued i imulatio The applied eccetricity diturbace i ± 6µ m Accordig to pecificatio, maximum eccetricity i ± 7µ m If we coider optic gai a 3 µ m/ V, trackig error have to be cotrolled withi ± 3V to atify CD pecificatio I Fig 8(b), lead-lag cotroller doe ot atify the pecificatio The other atify the CD pecificatio Notice that Dual-DOB performace i better tha igle DOB 4 Experimetal Reult Fig 9 illutrate the experimetal etup TM3VC33 DP ad 6-bit ADC, DAC with KHz amplig rate are ued Fig how the experimetal reult, Fig (a) i the reult of applyig a lead-lag cotroller Fig (b) ad (c) are obtaied with the lead-lag cotroller with DOB, ad the lead-lag cotroller with Dual-DOB, repectively I the Fig, CH i trackig error ad CH i cotrol igal The cotrol igal of Fig (c) i maller tha the other The reao i that Dual-DOB i le eitive to meauremet

5 ICCA5 oie becaue complemetary eitivity fuctio peak of Dual-DOB i maller tha geeral DOB Through thi fact, we check that the mallet trackig error i occurred i Dual-DOB ytem ad verify effective diturbace rejectio performace of Dual-DOB Jue -5, KINTEX, Gyeoggi-Do, Korea pidle Motor Driver VCM Driver RF Iterface Fig 9 Experimetal etup Fig 6 eitivity Fuctio (a) Lead-Lag Cotroller Fig 7 Complemetary eitivity Fuctio Ditace [um] 5-5 Voltage [V] 5-5 (b) Diturbace Oberver Time [] (a) Output Diturbace Time [] (b) Lead-Lag Cotroller 5 5 Voltage [V] Voltage [V] Time [] (c) DOB Time [] (d) Dual-DOB Fig 8 Diturbace ad Trackig Error (c) Dual Diturbace Oberver Fig Experimetal Reult

6 ICCA5 5 CONCLUION I thi paper, a dual diturbace oberver wa propoed to reduce the effect of cro-couplig i multi loop DOB ytem It wa poible for u to improve the eitivity fuctio with additioal exteral DOB with hardly affectig complemetary eitivity fuctio Deig of iteral DOB loop ad exteral loop DOB were idepedetly made o that we preveted traiet repoe quality from degradig while improvig the eitivity fuctio The propoed Dual-DOB wa applied to a commercial optical dik drive trackig ervo ytem The experimetal reult howed that the Dual-DOB i a effective method i rejectig the diturbace a well a improvig the trackig performace REFERENCE [] K Ohihi, A ew ervo method i mechatroic Tra Jp oc Elect Eg, vol 7-D, pp 83-86, 987 [] K Ohihi, M Nakao, K Ohihi ad K Miyachi, Microproceor cotrolled DC motor for load-ieitive poitio ervo ytem, IEEE Tra Idutrial Electroic, vol 34, pp 44-49, Feb 987 [3] K Ohihi, K Ohihi ad K Miyachi, Adaptive DC ervo Drive Cotrol Trackig Force Diturbace uppreio ito Accout, IEEE Tra o Id Applicatio, vol 4, No, pp 7-76, Ja/Feb 988 [4] M hahruz, Performace ehacemet of a cla of oliear ytem by diturbace oberver, IEEE/AME Tra o Mechatroic, vol 5, pp 39-33, ep [5] M hahruz, C Cloet ad M Tomizuka, uppreio of effect of oliearitie i a cla of oliear ytem by diturbace oberver, Proceedig of America Cotrol Coferece, vol 3, pp , [6] Y J Choi, K J Yag, W K Chug, H R Kim, I H uh, "Deig of Diturbace Oberver Coiderig Robute ad Cotrol Performace(): Aalyi o ecod Order ytem," Joural of Cotrol Automatio ad ytem Egieerig, vol 8, No 8, pp , Aug [7] Komada, N Machii, T Hori, Cotrol of Redudat Maipulator Coiderig Order of Diturbace Oberver, IEEE Tra Id Electro, vol 47, No, pp 43-49, Apr [8] B K Kim, W K Chug, Advaced Deig of Diturbace Oberver for High Performace Motio Cotrol ytem, Proceedig of the America Cotrol Coferece Achorage, AK pp -7 May 8-, [9] B K Kim, W K Chug, Performace Predictable Deig of Robut Motio Cotroller for High-Preciio ervo ytem, Proceedig of the America Cotrol Coferece Arligto, VA pp Ju 5-6, [] J Ueda, A Imagi ad H Tamayama, Track Followig Cotrol of Large Capacity Flexible Dik Drive with Diturbace Oberver Uig Two Poitio eor, Proc It Cof Advaced Itelliget Mechatroic, pp 44-49, 999 [] K Fujiyama, M Tomizuka, R Katayama, Digital trackig cotroller deig for CD player uig diturbace oberver, IEEE, pp , 998 [] K J Yag, Y J Choi, W K Chug, I H uh, R Oh, Jue -5, KINTEX, Gyeoggi-Do, Korea "Robut trackig cotrol of optical dik drive ytem uig error baed diturbace oberver ad it performace meaure," Proceedig of America Cotrol Coferece, vol, pp 395-4, [3] J Kwo, W K Chug, "Robut performace of the multiloop perturbatio compeator," Mechatroic, IEEE/AME Tra o Mechatroic, vol 7, pp 9-, Ju [4] H T Choi, I H uh, "Diturbace Oberver baed Iteral Model Cotroller Deig: Applicatio to trackig Cotrol of Optical Dik Drive," T KIEE vol 48A, No, pp 59-66, Feb 999 [5] H Lee ad M Tomizuka, Robut motio cotroller deig for high-accuracy poitioig ytem, IEEE Tra Idutrial Electroic, vol 43, o, pp Feb 996